June 18 (Bloomberg) -- Even as Democratic Party leaders denounce billionaire Republicans Charles and David Koch for filling the airwaves with misleading commercials, they’re also playing with the facts.

PolitiFact, a St. Petersburg, Florida-based group that tests the accuracy of political commercials, checked six ads sponsored by the Senate Majority PAC, a Democratic super-political action committee that aims to keep the party in control of the chamber. It found four of the group’s spots to be “false” or “mostly false” and another “half true.” Only one was deemed “mostly true.”

“The Democrats ceded the high ground,” said Sheila Krumholz, the executive director of the Center for Responsive Politics, a Washington-based nonprofit that tracks campaign spending. “There is really no reluctance to embrace outside groups and all the opportunities that outside groups present, including this messaging that is not really defensible.”

A review of Democratic outside organizations shows they’re turning to their own lineup of billionaire donors, creating a secretive network and airing streams of misleading television commercials.

And by some measures, they’re surpassing their Republican counterparts: Democratic super-PACs have outraised their rivals $114 million to $71 million, according to data from the Center for Responsive Politics. The Democratic sum easily surpasses such fundraising in the 2010 midterm elections, when the Senate Majority PAC raised just $4 million.

Six Seats

With the primary season waning and attention turning to the November elections in which control of the U.S. Senate is at stake, the onslaught from both sides will intensify. Republicans need a net gain of six seats to take the chamber, and both sides are bracing for showdowns in about a dozen states that could tip the balance of power in Congress.

Senate Majority Leader Harry Reid has tried to make the Kochs’ spending on behalf of Republicans an issue in the campaign, calling the energy executives “un-American” and accusing them of trying to buy elections and peddling commercials filled with “lies.”

“Just because you have huge amounts of money, you should not be able to run these false, misleading ads by the hundreds of millions of dollars,” Reid, of Nevada, said on the U.S. Senate floor in February.

In an interview and in testimony on Capitol Hill, Reid was unapologetic about his party’s parroting of its partisan adversaries’ approach.

Dueling Billionaires

“The decision of the Supreme Court has left the American people with a status quo in which one side’s billionaires are pitted against the other side’s billionaires,” said Reid, referring to a 2010 ruling that helped open the way for unlimited spending in campaigns.

The ruling created a political system where conflicting sides “argue all day and all night, weekends, forever, about whose billionaires are right, whose billionaires are wrong,” Reid said while testifying in favor of a constitutional amendment to limit political spending.

Asked why his party opted to engage in such a system, he said, “We can’t disarm.”

“There clearly is a double standard and hypocrisy,” said Senator John Cornyn of Texas, the former chairman of the National Republican Senatorial Committee, which helps party candidates for the chamber.

‘Intimidation’ Factor

“It is an intimidation effort,” Cornyn said. By attacking Republican donors, “they’re hoping that other people will not want that kind of publicity and negative attention so they will simply sit down and shut up and not speak their mind and exercise their constitutional rights.”

Reid’s stamp is on some of the most successful Democratic outside groups.

Susan McCue, his former chief of staff, runs the Senate Majority PAC, and Reid has solicited money on its behalf. The super-PAC raised $26 million through the end of May for the November elections with the help of billionaires such as former money manager Tom Steyer and Michael Bloomberg, the founder and majority owner of Bloomberg News parent Bloomberg LP. Financier George Soros is also a giver.

The House Majority PAC, another Democratic group, has amassed $13 million. Three more Democratic groups round out the top five super-PACs in funding so far this election, according to the Center for Responsive Politics.

Rove’s Group

American Crossroads, advised by Karl Rove, a onetime top political aide to former President George W. Bush, heads the Republican list of super-PACs, having raised $9.4 million.

The list doesn’t include Americans for Prosperity, a Republican-aligned group founded by the Koch brothers in 2004. It’s organized as a nonprofit, meaning it doesn’t disclose donors and is restricted from spending more than half its budget on direct election activities such as commercials that explicitly promote a candidate.

The group has broadcast 25,484 “issues ads” -- spots that almost all pan a Democratic candidate or politician for supporting President Barack Obama’s health-care law, according to New York-based Kantar Media’s CMAG data through June 16. AFP officials say they’ve spent $37 million since last fall and have a budget of at least $125 million for the midterm elections.

Targeting Tillis

One of the more glaring examples of an inaccurate ad is one by the Senate Majority PAC that has run in the North Carolina race between Democratic Senator Kay Hagan and Republican challenger Thom Tillis. The spot, broadcast 2,543 times through June 16 accuses Tillis, the state House speaker, of raising taxes on 80 percent of the state’s residents. In fact, the legislation has led to higher taxes on about 35 percent of taxpayers while cutting them for 45 percent.

Another one by the group, which the Washington Post called “nonsensical,” says a Republican Senate candidate in Louisiana trying to unseat Democratic incumbent Mary Landrieu is backed forces that supported exorbitant flood-insurance bills. In reality, Bill Cassidy championed an effort to undo the rate surges.

Another spot attacks New Hampshire Senate candidate Scott Brown for voting to support the oil industry on a key bill -- even though two Democratic senators backed by the PAC, Landrieu and Mark Begich of Alaska, cast their votes the same way.

One of the few claims by the Senate Majority PAC deemed by fact-checkers to be true doesn’t focus on policy at all: It’s an ad running in North Carolina that centers on relationships that two of Tillis’s staff members had with lobbyists.

Negative Ads

Less than 10 percent of the 20,592 commercials that the Senate Majority PAC has funded this election cycle carry “positive” messages, according to CMAG’s data. For the House Majority PAC, about 84 percent of its 6,677 commercials project negative images.

That’s on par with the Koch-founded Americans for Prosperity, which has aired 89 percent negative commercials this cycle.

“Harry Reid’s in a difficult position,” said Harvard Law School Professor Larry Lessig, who started a super-PAC focused on campaign-finance reform. “It’s hard to see the difference between what he’s attacking and what he’s doing.”

As much as Reid and other Democrats decry the secrecy of such groups as Americans for Prosperity, Democrats for a decade have been building and refining their own network of undisclosed donors.

The most visible is Patriot Majority USA, which is run by another former top aide to Reid.

Patriot Majority raised $23 million in 2012, according to its most recent tax forms, and so far this election cycle has aired almost 6,500 ads pummeling Republican candidates in Arkansas, Arizona, Florida, Kentucky, Louisiana, North Carolina and Washington, CMAG data shows.